Hydraulic fracturing is a method for increasing fluence and recovery rates of fluids from subterranean reservoir rock formations whereby rock layers are fractured using pressurized fluids. After drilling a wellbore, a fracture or field of fractures is initiated along the wellbore by pumping a fracturing fluid, such as a gel/water mixture, into the wellbore at a very high rate. A proppant is introduced into the fracturing fluid to prop the fractures open when the fracturing fluid pressure is removed. The proppant typically includes hard particulate material, such as sand, concrete, or rock. The propped open fractures act as relatively high conductivity routes through which the reservoir fluid (e.g., oil or natural gas) can flow to the wellbore.
Because the preferred fracture planes of the reservoir rock formations are highly variable and difficult to predict, the location and shape of the fracture field resulting from a hydraulic fracture is essentially unknown. Knowledge of the location and paths of the fractures would be useful in a number of areas, including locating successive drilling locations to optimize reservoir coverage. Some techniques have been developed to estimate the path of the hydraulic fractures, including radioactive proppant tracing (which has environmental constraints), microseismic monitoring, and tiltmetering. However, accurate interrogation of the fractures and determination of the contents continues to be a major concern.